Since the 1980's wireless networks for mobile communications have become more and more pervasive across the world. While the technical elements of the network (such as RF equipment, antennas and radios, and the like) have continued to evolve, the design of antenna supporting structures (or towers) has remained pretty much unchanged. The towers, whether self-supporting, guyed or of monopole type, have served the industry well through the ongoing evolution of network architecture, however, the modification of these existing tower structures to increase structural capacity is become more and more commonplace.
In order to support heavier and often more numerous antennas required by the current build out of LTE (Long Term Evolution) or 4G networks, the industry must find new and creative ways to add capacity to existing tower structures.
The more common tower type built in densely populated urban areas was the monopole. These monopoles are usually multi-sided tapered tubular structures with a very small profile and hence more attractive from a siting approval standpoint. These are also the more difficult to augment or modify structurally since the bolting of additional structural elements must be done from the outside as they are too narrow to access from the inside.
A common method of strengthening these monopoles has been the addition of steel elements to the pole shafts. This can be accomplished by adding flat plates or other structural steel shapes to the “flats or flat sides” of the multi-sided structures.
One aspect of these installations that has often been overlooked or misunderstood is the proper transfer of the forces from the additional steel elements to the foundation. In some instances of flat plate installation, the lower end is terminated simply by welding the flat plates directly to the base plate or in some cases directly on top of the original base plate weld, ignoring the effect to the base plate and the anchor bolts. Neither of these termination methods have been fully investigated possibly making these types of installations ineffective and unreliable.
Another method is to terminate by welding the flat plates to the pole shaft well above the base plate and to add vertical stiffener plates adjacent to new plates. This design, while more effective requires the proper spacing of both the flat plates and the vertical stiffeners and often results in total weld lengths of more than 20 ft. per location. This excessive field welding is not only costly, but is often difficult to complete to an adequate level of quality.